Numerical control system and motor drive controller

ABSTRACT

A numerical control system according to the present invention controls machine drive systems included in a machine tool that performs machining using a tool, according to a numerical control program, and includes a coordinate transformation unit that acquires a disturbance force or a disturbance torque applied to each machine drive system, and coordinate-transforms the disturbance force or the disturbance torque into a tool reference coordinate system for output, and an identification unit that calculates cutting process parameters that determine characteristics of a cutting process model and dynamic characteristic parameters that determine characteristics of a dynamics model of the machine tool, using the disturbance force or the disturbance torque output from the coordinate transformation unit, states of the machine drive systems, predetermined equation models, and cutting conditions. The equation models define relationships between the cutting process parameters, the dynamic characteristic parameters, and the disturbance force or the disturbance torque.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/JP2017/031261, filedAug. 30, 2017, the entire contents of which are incorporated herein byreference.

FIELD

The present invention relates to a numerical control system and a motordrive controller for controlling a machine tool.

BACKGROUND

A machine tool is a machining apparatus for removal machining that ismachining to remove unnecessary portions from a workpiece by applyingforce or energy to the workpiece using a tool. In particular, incutting, which is one type of removal machining, a tooth edge of a toolis brought into contact with a workpiece at a high cutting speed,causing shear fracture on a workpiece surface, and scraping off anunnecessary portion of the workpiece.

Cutting is a physical phenomenon in which a cutting process andmechanical dynamics influence each other. Thus, it is desirable tomanage both simultaneously to manage a machining state. Here, a cuttingprocess represents a series of steps in which a tool tooth edge enters aworkpiece, forming a machined surface while producing chips. Mechanicaldynamics represent the behavior of structures constituting a machinewhen the mechanical structures are vibrated by a vibration source insideor outside the machine tool. In general, cutting is a phenomenon inwhich various physical phenomena including the above-described cuttingprocess and mechanical dynamics complexly influence each other. Thus,integrated analysis thereof is considered to be difficult. Therefore, inproduction sites, objects to be evaluated are limited to achievemachining management depending on the purpose.

For example, a method is used which evaluates a position deviation of atool produced with respect to an ideal trajectory by measuring machinedworkpiece dimensions, and adjusts depth or width of cutting so that theworkpiece falls within desired accuracy. In another example, a method isused which evaluates the wear width of a tool tooth edge after machiningfor a predetermined time or by a predetermined distance, to search for acutting speed that allows the tool to have extended life whilemaintaining machining quality. In still another example, a method isused which acquires detection signals from a force sensor added to amachine, to determine a spindle drive system rotation speed or a feedrate at which cutting load does not become excessive. In still anotherexample, a method is used which observes the shape or dischargeddirection of chips produced during machining, to adjust cutting speedand cutting amount.

However, by the evaluation methods of the above methods which performevaluation using results measured during non-machining, evaluatedobjects are not in the same state as those during machining. Thus, themeasurement results do not represent an actual machining. For a cuttingprocess in which a plurality of physical phenomena influence each other,it is desirable to analyze and evaluate a machining state duringmachining, i.e. in-process. As a method of managing a machining statein-process, Patent Literature 1 proposes the following method.

In the method described in Patent Literature 1, machining performed by amachine tool at which a force sensor is installed is simulated, asimulated cutting force is compared with a measured value of the forcesensor, and cutting process information for calculating a cutting forceby simulation is corrected to estimate a final cutting force. Thismethod can calculate a value reflecting a machining state because thecutting process information is updated, using a cutting force obtainedduring actual machining.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No.2013-061884

SUMMARY Technical Problem

However, in the method described in Patent Literature 1, only thecutting process information is calculated, using dynamic characteristicinformation on a tool stored in advance. Thus, there is a problem inthat if the dynamic rigidity of a structure in the machine has changedduring machining, displacement cannot be calculated correctly. It isknown that generally, the dynamic rigidity of a spindle drive systemchanges due to heat generation in the spindle drive system, and thedynamic rigidity of a workpiece changes due to a decrease in theworkpiece mass caused by cutting. The method described in PatentLiterature 1 that does not take mechanical dynamics into account thushas a problem in that it cannot accurately identify a cutting processand mechanical dynamics that change successively during machining.

The present invention has been made in view of the above. It is anobject of the present invention to provide a numerical control systemthat can accurately identify a cutting process and mechanical dynamics.

Solution to Problem

A numerical control system according to an aspect of the presentinvention is a numerical control system that controls machine drivesystem included in a machine tool that performs machining using a tool,according to a numerical control program, and includes a coordinatetransformation unit that acquires a disturbance force or a disturbancetorque applied to each of the machine drive systems, andcoordinate-transforms the disturbance force or the disturbance torqueinto a tool reference coordinate system for output. The numericalcontrol system further includes an identification unit that calculatescutting process parameters that determine characteristics of a cuttingprocess model and dynamic characteristic parameters that determinecharacteristics of a dynamics model of the machine tool, using thedisturbance force or the disturbance torque output from the coordinatetransformation unit, states of the machine drive systems, predeterminedequation models, and cutting conditions. The equation models definerelationships between the cutting process parameters, the dynamiccharacteristic parameters, and the disturbance force or the disturbancetorque.

Advantageous Effects of Invention

The numerical control system according to the present invention has anadvantage of being able to accurately identify a cutting process andmechanical dynamics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of anumerical control system according to a first embodiment.

FIG. 2 is a flowchart illustrating an example of an operation procedurein the numerical control system of the first embodiment.

FIG. 3 is a diagram illustrating relationships between coordinatesystems in the first embodiment.

FIG. 4 is a schematic diagram illustrating a state where a disturbanceforce is transmitted to a table when a workpiece fixed to the tablevibrates due to a cutting force in the first embodiment.

FIG. 5 is a diagram illustrating an example of a rotation angle of atool with a tool tooth edge contacting the workpiece in the firstembodiment.

FIG. 6 is a diagram illustrating an example of a rotation angle of thetool with tool tooth edges not contacting the workpiece in the firstembodiment.

FIG. 7 is a diagram illustrating a state of cutting at a first toothedge when a deviation is produced between the tool center and thespindle drive system center in the first embodiment.

FIG. 8 is a diagram illustrating a state of cutting at a second toothedge when a deviation is produced between the tool center and thespindle drive system center in the first embodiment.

FIG. 9 is a diagram illustrating a configuration example of a processingcircuit in the first embodiment.

FIG. 10 is a diagram illustrating a configuration example of a numericalcontrol system according to a second embodiment.

FIG. 11 is a block diagram illustrating a configuration example of adisturbance estimation unit in a third embodiment.

FIG. 12 illustrates an example of a machine drive system model in thethird embodiment.

FIG. 13 is a diagram illustrating disturbance force estimation resultsin a comparative example.

FIG. 14 is a diagram illustrating an example of a disturbance forceestimated by the disturbance estimation unit in the third embodiment.

FIG. 15 is a block diagram illustrating a configuration example of adisturbance estimation unit in a fourth embodiment.

FIG. 16 is a diagram illustrating an example of feed machine drivesystem modeling in the fourth embodiment.

FIG. 17 is a block diagram illustrating a configuration example of adisturbance estimation unit in a fifth embodiment.

FIG. 18 is a block diagram illustrating a configuration example of anumerical control system according to a sixth embodiment.

FIG. 19 is a block diagram illustrating another configuration example ofthe numerical control system according to the sixth embodiment.

FIG. 20 is a block diagram illustrating a configuration example of anumerical control system according to a seventh embodiment.

FIG. 21 is a block diagram illustrating another configuration example ofthe numerical control system according to the seventh embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a numerical control system and a motor drive controlleraccording to embodiments of the present invention will be described indetail with reference to the drawings. The embodiments are not intendedto limit the invention.

First Embodiment

FIG. 1 is a block diagram illustrating a configuration example of anumerical control system according to a first embodiment of the presentinvention. A numerical control system 1 of the first embodiment controlsa machine tool 2.

The machine tool 2 includes a machine drive system 21 and a machinedrive system 22. The machine drive system 21 and the machine drivesystem 22 each include a motor and one or more structures connected tothe motor. The machine drive system 22 is a spindle drive system thatimparts rotational motion to a tool. The machine drive system 21 is afeed drive system that gives a position to the tool. The machine drivesystem 22 and the machine drive system 21 are controlled insynchronization. The machine drive system 21 as the feed drive systemincludes, for example, a servomotor, a coupling, a ball screw, and atable. The machine drive system 22 as the spindle drive system includes,for example, a spindle motor, a gear, a shaft, and a tooling system. Themachine tool 2 rotates a tool attached to the machine drive system 22 asthe spindle drive system, to perform cutting on a workpiece fixed on thetable of the machine drive system 21 as the feed drive system. Themachine drive system 21 and the machine drive system 22 are an exampleof machine drive systems included in the machine tool 2 that performsmachining using a tool. The configurations of the machine drive system21 and the machine drive system 22 are not limited to theabove-described examples. Although FIG. 1 illustrates one machine drivesystem 21 as a feed drive system, the number of feed drive systems maybe one or more.

The servomotor of the machine drive system 21 and the spindle motor ofthe machine drive system 22 each include a rotary encoder, and output anencoder signal that is a signal detected by the rotary encoder to thenumerical control system 1. The machine drive system 21 detects a motorcurrent applied to the servomotor, and outputs a detection result as amotor current signal to the numerical control system 1. The machinedrive system 22 detects a motor current applied to the spindle motor,and outputs a detection result as a motor current signal to thenumerical control system 1.

The numerical control system 1 controls the machine drive system 21 andthe machine drive system 22 according to a Numerical Control (NC)program provided from outside or held inside.

The NC program includes a position command of a relative tool positionor a feed drive system in a predetermined coordinate system, a spindledrive system rotation speed command, and a feed rate command. Theabove-described coordinate system used in the NC program is referred toas an NC program coordinate system. The NC program coordinate system isa coordinate system fixed to a workpiece, for example.

As illustrated in FIG. 1 , the machine drive system 21 is provided withan acceleration sensor 211, and the machine drive system 22 is providedwith an acceleration sensor 221. The acceleration sensor 211 detectsacceleration in the machine drive system 21 in a linear direction or arotation direction, and outputs a detection result as an accelerationsensor signal to the numerical control system 1. The acceleration sensor221 detects acceleration in the machine drive system 22 in a lineardirection or a rotation direction, and outputs a detection result as anacceleration sensor signal to the numerical control system 1. Theacceleration sensor 211 and the acceleration sensor 221 may be includedin the numerical control system 1. The acceleration sensor 211 and theacceleration sensor 221 are an example of sensors that detect the speedor acceleration of the machine drive systems 21 and 22.

As illustrated in FIG. 1 , the numerical control system 1 includes acommand value generation unit 11, a coordinate transformation unit 12,machine drive control units 13 and 15, disturbance estimation units 14and 16, an identification unit 17, and a storage unit 18. The storageunit 18 stores a dynamics model, a cutting process model, and cuttingconditions. The dynamics model, the cutting process model, and thecutting conditions will be described later. The machine drive controlunits 13 and 15 and the disturbance estimation units 14 and 16constitute a motor drive controller 100.

FIG. 2 is a flowchart illustrating an example of an operation procedurein the numerical control system 1 of the first embodiment. The operationof the numerical control system 1 of the first embodiment will bedescribed with reference to FIGS. 1 and 2 .

The command value generation unit 11 analyzes commands described in theNC program, and calculates drive commands for the machine drive systems(step S1). The command value generation unit 11 outputs the calculateddrive commands to the machine drive control units 13 and 15. Further,the command value generation unit 11 outputs, to the coordinatetransformation unit 12, setting information on the NC program coordinatesystem, the relative tool position and the tool rotation angle in thecoordinate system, and the drive commands for the machine drive systems.The setting information on the NC program coordinate system, and therelative tool position and the tool rotation angle in the coordinatesystem are described in the NC program.

The machine drive control units 13 and 15 control the machine drivesystems according to the drive commands calculated by the command valuegeneration unit 11 (step S2). Specifically, the machine drive controlunit 13 controls the motor current so that the encoder signal outputfrom the rotary encoder of the servomotor of the machine drive system 21follows the drive command representing a target value. The machine drivecontrol unit 15 controls the motor current so that the encoder signaloutput from the rotary encoder of the spindle motor of the machine drivesystem 22 follows the drive command representing a target value.Further, each of the machine drive control units 13 and 15 outputs, tothe identification unit 17 described later, a machine drive system statethat is information including a position command, position feedback, avelocity command, and velocity feedback of corresponding one of themachine drive systems. Operations in the machine drive control units 13and 15 are general operations in accordance with the drive commands, andthus will not be described in detail.

The disturbance estimation unit 14 and the disturbance estimation unit16 estimate disturbances in the machine drive system 21 and the machinedrive system 22, respectively (step S3). Specifically, the disturbanceestimation unit 14 estimates and outputs a disturbance force applied tothe machine drive system 21 as a disturbance force acting on a feeddrive system, using the encoder signal and the motor current signaloutput from the machine drive system 21, and the acceleration sensorsignal output from the acceleration sensor 211. Specifically, thedisturbance force is estimated, regarding the feed drive system as asingle inertia drive system, using the following formula (1).F _(d1) =K ₁ I ₁ −Ma  [Formula 1]F_(d1): disturbance force acting on a machine drive system,K₁: torque constant, I₁: motor current,M: mass of machine drive system, a: acceleration

A method of estimating the disturbance force acting on a feed drivesystem is not limited to the above-described example. For example, thedisturbance estimation unit 14 may calculate, as an estimateddisturbance force, the result of formula (1) from which a viscousfrictional force proportional to the speed of the machine drive systemis subtracted.

The disturbance estimation unit 16 estimates and outputs a disturbanceforce applied to the spindle drive system as a disturbance force actingon the spindle drive system, using the encoder signal and the motorcurrent signal output from the machine drive system 22, and theacceleration sensor signal output from the acceleration sensor 221. Thedisturbance estimation unit 16 estimates a disturbance force applied tothe machine drive system 22 using a detection result detected by asensor that detects the velocity or acceleration of the machine drivesystem 22. Specifically, the acceleration sensor signal is convertedinto angular acceleration, and the disturbance force acting on thespindle drive system is estimated using the following formula (2) withregarding the spindle drive system as a single inertia drive system.

[Formula 2]

$F_{d2} = \frac{{K_{2}I_{2}} - {J\;\overset{.}{\omega}}}{r}$F_(d2): disturbance force acting on a spindle drive system,K₂: torque constant, I₂: motor current,J: main spindle axial inertia,{dot over (ω)}: angular acceleration, r: tool radius

A method of estimating the disturbance force acting on the spindle drivesystem is not limited to the above-described example. For example, thedisturbance estimation unit 16 may calculate, as an estimateddisturbance force, the result of formula (2) from which a viscousfrictional force proportional to the angular velocity of the machinedrive system is subtracted. The disturbance estimation unit 16 maycalculate and output an estimated disturbance torque instead of theestimated disturbance force.

Returning to the description of FIG. 2 , next, the coordinatetransformation unit 12 coordinate-transforms the disturbance forceacting on the feed drive system calculated by the disturbance estimationunit 14 and the disturbance force acting on the spindle drive systemcalculated by the disturbance estimation unit 16, based on the settinginformation on the NC program coordinate system and the relative toolposition and the tool rotation angle in the NC program coordinate systemoutput from the command value generation unit 11, into a tool referencecoordinate system for output (step S4). That is, the coordinatetransformation unit 12 acquires the disturbance forces or disturbancetorques applied to the machine drive systems 21 and 22, andcoordinate-transforms the disturbance forces or disturbance torques intothe tool reference coordinate system for output. In the firstembodiment, the coordinate transformation unit 12 acquires disturbanceforces or disturbance force vectors of the machine drive systems fromthe disturbance estimation units 14 and 16.

Here, the tool reference coordinate system is a coordinate systemincluding a tool axis direction and other two directions in a planeperpendicular to the tool axis direction, and, for example, is acoordinate system with reference to the tool in which the tool axisdirection is aligned with the Z axis, a tool traveling direction in aplane perpendicular to the tool axis direction is the X axis, and adirection perpendicular to the X axis and the Z axis is the Y axis. Thetool reference coordinate system is a coordinate system that istranslated with the translation of the tool, but is a coordinate systemthat does not consider rotation with the rotation of the tool. The toolreference coordinate system is not limited to the above-describedexample, and may be any coordinate system including a tool axisdirection and other two directions in a plane perpendicular to the toolaxis direction. The disturbance force acting on the spindle drive systemis a quantity that varies in force direction depending on the toolrotation angle, unlike the disturbance force acting on the feed drivesystem. Thus, the coordinate transformation of the spindle drive systemdisturbance force is executed on each tool rotation angle.

Specific processing in the coordinate transformation unit 12 will bedescribed with reference to FIG. 3 . FIG. 3 is a diagram illustratingthe relationships between coordinate systems in the first embodiment. Inthe example illustrated in FIG. 3 , a workpiece 32 is placed on a table31 that constitutes the machine drive system 21, and a tooling system 34that constitutes the machine drive system 22 holds a tool 33. The table31 is driven by the servomotor (not illustrated), and the tooling system34 is driven by the spindle motor (not illustrated). A coordinate systemX-Y-Z is the tool reference coordinate system, a coordinate systemX′-Y′-Z′ is the NC program coordinate system, and a coordinate systemX″-Y″-Z″ is a machine coordinate system. A direction 35 indicates adirection of relative displacement of the front end of the workpiece 32with respect to the table 31.

The coordinate transformation unit 12 sets the tool reference coordinatesystem X-Y-Z, using the setting information on the NC program coordinatesystem and relative tool position information. Further, the coordinatetransformation unit 12 coordinate-transforms the estimated disturbanceforce acting on the feed drive system calculated by the disturbanceestimation unit 14 into an estimated disturbance force in the toolreference coordinate system X-Y-Z, and outputs it to the identificationunit 17. The coordinate transformation unit 12 may coordinate-transformsthe estimated disturbance force of the spindle drive system calculatedby the disturbance estimation unit 16 into an estimated disturbanceforce in the tool reference coordinate system, and output it to theidentification unit 17.

Because the estimated disturbance force acting on the feed drive systemand the estimated disturbance force acting on the spindle drive systemeach include components in the X direction and the Y direction in thetool reference coordinate system, the coordinate transformation unit 12can determine an estimated disturbance force to be output to theidentification unit 17 by performing the following processing on the Xdirection and the Y direction. For example, the coordinatetransformation unit 12 takes the mean values of the components in the Xdirection and the Y direction, and adds a Z axis component of thedisturbance force acting on the feed drive system to the mean values, tooutput them as an estimated disturbance force to the identification unit17. As another example, a machine drive system to be used for anestimated disturbance force may be set in advance for each machiningpath, and an estimated disturbance force corresponding to the machinedrive system may be coordinate-transformed and output. As still anotherexample, the mean values of the X-axis components and the Y-axiscomponents of the disturbance force acting on the feed drive system andthe disturbance force acting on the spindle drive system may becalculated, and the mean values may be used as an estimated disturbanceforce. As still another example, the coordinate transformation unit 12may set in advance a determination lower limit and a determination upperlimit on each of the X axis components and the Y axis components for thedisturbance force acting on the feed drive system and the disturbanceforce acting on the spindle drive system, and use, as an estimateddisturbance force, the X-axis component or the Y-axis component of thedisturbance force acting on the feed drive system or the disturbanceforce acting on the spindle drive system that is higher than or equal tothe corresponding determination lower limit and lower than or equal tothe corresponding determination upper limit. When the acquireddisturbance forces or disturbance torques include components in the samedirection on tool reference coordinates, the coordinate transformationunit 12 may select a combination in which directions are independentfrom each other out of the acquired disturbance forces or disturbancetorques. As still another example, the degree of reliability may be setfor each machine drive system, and a machine drive system with a higherdegree of reliability may be used for coordinate transformation. It isknown that estimation accuracy of a multi-inertia drive system isgenerally lower than that of a single-inertia drive system. Therefore,for example, by setting the reciprocal of the number of inertial bodiesconstituting a machine drive system as the degree of reliability, amachine drive system with a simple structure can be preferentially used.As another example of a reliability degree setting method, by settingthe degree of reliability of a machine drive system close to a machiningpart high, and setting the degree of reliability of a machine drivesystem far from the machining part low, the machine drive systemsusceptible to cutting force produced at the machining part can bepreferentially used. As another example of a reliability degree settingmethod, by setting the degree of reliability of a machine drive systemto a value higher than zero when the machine drive system is driving,and setting the degree of reliability of a machine drive system to zerowhen the machine drive system is at rest, the driving machine drivesystem can be preferentially used. The above reliability degree settingmethods can also be used in combination. Reliability degree settingmethods are not limited to those above.

Returning to the description of FIG. 2 , the identification unit 17calculates parameters such as dynamic characteristic parameters thatdetermine the characteristics of the dynamics model and cutting processparameters that determine the characteristics of the cutting processmodel (step S5). Specifically, the identification unit 17 calculatesdynamic characteristic parameters that determine the characteristics ofthe dynamics model and cutting process parameters that determine thecharacteristics of the cutting process model, using the estimateddisturbance force or estimated disturbance torque output from thecoordinate transformation unit 12, the machine drive system statesoutput from the machine drive control units 13 and 15, and the cuttingconditions, the dynamics model, and the cutting process model stored inthe storage unit 18. Here, the dynamic characteristic parameters areparameters that determine the characteristics of the dynamics model tobe described later, such as a damping coefficient, a natural frequency,a mass, and a vibration mode vector. The cutting process parameters areparameters that determine the characteristics of the cutting processmodel to be described later, such as a specific cutting resistance, anedge force, a tool eccentricity, and a tool wear width.

As the cutting conditions, information is set which includes a feedrateper tooth, a tool diameter, the number of tool teeth, a tool torsionangle, an axial depth of cutting, a radial depth of cutting, a workpiecematerial shape, and a cutting mode indicating up-cut or down-cut.

The dynamics model is a mathematical model that describes the dynamiccharacteristics of mechanical structures inside the machine tool 2.Hereinafter, an example of the dynamics model will be described. FIG. 4is a schematic diagram illustrating a state where a disturbance force istransmitted to the table 31 when the workpiece 32 fixed to the table 31vibrates due to a cutting force in the first embodiment. Like theexample illustrated in FIG. 3 , FIG. 4 is premised on a configurationexample in which the workpiece 32 is placed on the table 31 of themachine drive system 21, and the tooling system 34 of the machine drivesystem 22 holds the tool 33. In FIG. 4 , a relative displacement 36indicates a relative displacement of the front end of the workpiece 32in a vibration mode vector direction with respect to the table 31, acutting force 37 indicates the cutting force in the workpiece 32, and adisturbance force 38 indicates the disturbance force transmitted to thetable 31. The relationships between the cutting force 37, thedisturbance force 38, and the relative displacement 36 at this time canbe expressed by the following formula (3). The dynamics modelrepresented in formula (3) is a mathematical model for calculating adisturbance force transmitted to a machine drive system through amechanical structure including a tool or a workpiece when a cuttingforce is produced, and calculating a position deviation produced at eachmachine drive system through the mechanical structure when the cuttingforce is produced.f _(c) =m _(t) {umlaut over (x)}+c _(t) {dot over (x)}+k _(t) xf _(d) =c _(t) {dot over (x)}+k _(t) x  [Formula 3]f_(c): cutting force, f_(d): disturbance force,m_(t): equivalent mass, c_(t): equivalent damping coefficient,k_(t): equivalent spring constant,x: relative displacement of cutting part of workpiece in vibration modevector direction with respect to table

The dynamics model illustrated in formula (3) is a model in which theworkpiece 32 on the table 31 is described as a one-degree-of-freedomvibration system, but the dynamics model is not limited to the aboveexample. For example, the dynamics model may be described as amulti-degree-of-freedom vibration system including a fixing portion forfixing the workpiece 32 and the table 31. Further, a dynamics model onthe tool-side structure including the tool 33, the tooling system 34,and the spindle motor may be set. Furthermore, a dynamics model may beset as a vibration system in which the workpiece 32-side structure andthe tool 33-side structure are combined.

The cutting process model is a mathematical model that describes acutting process between the tool 33 and the workpiece 32. An example ofthe cutting process model is represented in the following formula (4).f _(c) =K ^(c) ah(φ(t))·g(φ(t))  [Formula 4]f_(c): cutting force, K^(c): specific cutting resistancea: axial depth of cutting, h: uncut chip thickness,φ: tool rotation angle, t: time

${g\left( {\varphi(t)} \right)} = \left\{ \begin{matrix}1 & \left( {\varphi_{s} \leq {\varphi(t)} \leq \varphi_{f}} \right) \\0 & \left( {{{\varphi(t)} < \varphi_{s}},{\varphi_{f} < {\varphi(t)}}} \right)\end{matrix} \right.$φ_(s): tool engage angle, φ_(f): tool disengage angle

The above formula (4) is a numerical formula for calculating a cuttingforce to be applied by the tool to the workpiece from an uncut chipthickness corresponding to a tool rotation angle at each time. Here, theuncut chip thickness refers to a thickness by which a tool tooth edgethat is a tooth edge of the tool 33 cuts the workpiece 32 when passingthrough the workpiece 32. As illustrated in FIGS. 5 and 6 , when a tooltooth edge is at an angle at which it contacts the workpiece 32, thecutting force is calculated to a value higher than or equal to zero, andwhen the tool tooth edge is at an angle at which it does not contact theworkpiece 32, the cutting force is calculated to zero. FIG. 5 is adiagram illustrating an example of the rotation angle of the tool 33 atwhich a tool tooth edge contacts the workpiece 32. FIG. 6 is a diagramillustrating an example of the rotation angle of the tool 33 at which notool tooth edges contact the workpiece 32. That is, it is determinedwhether a tooth edge contacts the workpiece 32 based on a positiondeviation at each rotation angle of the tool 33 or each time. When atool tooth edge contacts the workpiece 32, the uncut chip thickness iscalculated. When no tool tooth edges contact the workpiece 32, the uncutchip thickness is calculated to zero.

By performing the calculation illustrated in formula (4) on threedirections: a tangential direction, a radial direction, and an axialdirection of the tool, a cutting force in the three directions can becalculated. In the cutting process model, by multiplying a cutting forcehaving components in the three directions by a rotation matrixcorresponding to a tool rotation angle for coordinate transformation,the cutting force in the tool reference coordinate system is calculated.An example of the coordinate transformation is illustrated in formula(5).

$\begin{matrix}{\begin{bmatrix}F_{x}^{c} \\F_{y}^{c} \\F_{z}^{c}\end{bmatrix} = {\begin{bmatrix}{\cos\mspace{11mu}{\varphi(t)}} & {\sin\mspace{11mu}{\varphi(t)}} & 0 \\{{- \sin}\mspace{11mu}{\varphi(t)}} & {\cos\mspace{11mu}{\varphi(t)}} & 0 \\0 & 0 & 1\end{bmatrix}\begin{bmatrix}F_{t}^{c} \\F_{r}^{c} \\F_{a}^{c}\end{bmatrix}}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$F_(x) ^(c): cutting force in X-axis direction in tool referencecoordinate system,F_(y) ^(c): cutting force in Y-axis direction in tool referencecoordinate system,F_(z) ^(c): cutting force in Z-axis direction in tool referencecoordinate system,F_(t) ^(c): cutting force in tool tangential direction,F_(r) ^(c): cutting force in tool radial direction,F_(a) ^(c): cutting force in tool axial direction

By performing the calculations represented in the above formulas (4) and(5) for each tool tooth edge, a final cutting force is calculated. Thecutting process model illustrated in formula (4) is a mathematical modelfor calculating an uncut chip thickness, based on a tool rotation angleand a relative position between a tooth edge of a tool and a workpiecemachined by the tool, and calculating a cutting force produced betweenthe tool and the workpiece based on the uncut chip thickness. An uncutchip thickness in formula (4) can be calculated by formula (6) using afeedrate per tooth and a tool rotation angle.h(φ(t))=c sin φ(t)  [Formula 6]c: feedrate per tooth

As another example, an uncut chip thickness can also be calculated usingformula (7).h(φ(t))=c sin φ(t)+{ν(φ,t)−w(φ,t)}+Δr(φ,t,N _(tooth))ν: tool center displacement amount in tool radial direction,w: previous machined surface displacement amount in tool radialdirection,T: cutting cycle, Δr: correction amount corresponding to tooth edge of atool and tool rotation angle,N_(tooth): tooth number

Formula (7) is a formula for calculating an uncut chip thicknessobtained by adding, to formula (6), a variation calculated from thedifference between a current tool displacement and a previous machinedsurface, and further adding a correction amount corresponding to eachtool tooth edge. In the calculation illustrated in formula (7), an uncutchip thickness is corrected by the difference between the amount ofdisplacement that has given influence on the machined surface shapeamong the amounts of displacement that have been produced at tool toothedges one or more teeth before, and the amount of displacement that hasbeen produced at the current tool tooth edge. That is, the uncut chipthickness is calculated based on the difference between a trajectoryproduced by the current tool tooth edge involved in cutting and atrajectory of a tool tooth edge that has given influence on the machinedsurface shape from among tool tooth edges one or more teeth before thecurrent tool tooth edge. Here, the tool tooth edge one or more teethbefore is a tool tooth edge that has been involved in cutting at a timebefore a time at which a tool tooth edge is being involved in cutting.For example, in a tool with two teeth, when a tool tooth edge currentlycutting is a second tooth, a tool tooth edge one tooth before is a firsttooth before rotation through 180 degrees, a tool tooth edge two teethbefore is the second tooth before rotation through 360 degrees, and atool tooth edge three teeth before is the first tooth before rotationthrough 540 degrees. When the tool is displaced during cutting and thetooth edges temporarily move away from the workpiece, the current tooltooth edge cuts not only a previous machined surface produced by a tooltooth edge one tooth before but also a previous machined surfaceproduced by a tool tooth edge two or more teeth before.

Further, in the calculation illustrated in formula (7), an uncut chipthickness is corrected by a correction amount corresponding to a tooltooth edge number that is a number indicating a tool tooth edge and atool rotation angle. Here, the correction amount is introduced tocorrect a change in uncut chip thickness due to cutting by tool toothedges with different rotation radii. The following are examples wherethe correction amount needs to be introduced. For example, when wear orchipping of a tool occurs at a certain tooth edge of the tool, theradius of rotation of the tool tooth edge becomes shorter than that ofthe other tool tooth edge(s). Thus, a correction amount corresponding tothe wear width or chipping width of the tool is added. As anotherexample, when there is an error in tool tooth edge attachment in areplaceable tooth edge tool, a correction amount corresponding to theattachment error is added. As another example, when the spindle drivesystem center does not coincide with the tool center, that is, whenthere is a tool eccentricity, a correction amount corresponding to thetool eccentricity is added. The tool center is the center of thecircumscribed circle of the tool 33. The tool eccentricity is thecorrection amount of an uncut chip thickness for each tool tooth edge bythe amount of an increase or decrease in the radius of rotation of thetool tooth edge when an amount of misalignment is produced between thetool center and the spindle drive system center as illustrated in FIGS.7 and 8 . FIG. 7 is a diagram illustrating a state of cutting at thefirst tooth edge when an amount of misalignment is produced between thetool center and the spindle drive system center. FIG. 8 is a diagramillustrating a state of cutting at the second tooth edge when an amountof misalignment is produced between the tool center and the spindledrive system center. A first tooth edge 43 and a second tooth edge 44are the tooth edges of the tool 33. In the example illustrated in FIGS.7 and 8 , there is a misalignment between the tool center and thespindle drive system center 42. In this case, it is necessary to correctan uncut chip thickness with respect to an uncut chip thickness whenthere is no misalignment. The tool eccentricity indicates the correctionamount at this time. That is, the tool eccentricity corresponding to therotation angle of the tool is added to or subtracted from the uncut chipthickness. Examples of correcting an uncut chip thickness with acorrection amount are not limited to the above examples. The correctionamount may be changed appropriately according to a process occurring ata tooth edge.

The cutting process model is not limited to formula (4). For example,using formula (4), the value of the specific cutting resistance when thecutting speed is a high speed that is higher than or equal to athreshold may be changed from that when the cutting speed is a low speedthat is lower than the threshold. Further, a model in which an edgeforce component is added as a constant term to the right side of formula(4) may be used. Furthermore, a model in which a process damping forceis added to the right side of formula (4) may be used. Here, the processdamping force is a force produced by a flank face of a tool tooth edgecontacting a workpiece. As another example, a cutting process model fora tool with a torsion angle may be used. Specifically, a model may beused which divides a tool into tool segments of a small thickness in anaxial direction, calculates a cutting force at each small-thickness toolsegment, and adds up the cutting forces in the tool axis direction tocalculate a final cutting force. As still another example, a model thatcalculates an uncut chip thickness and a cutting force by finite elementanalysis may be used.

The following describes processing to identify an equivalent dampingcoefficient and an equivalent natural frequency as dynamiccharacteristic parameters, and identify a specific cutting resistance asa cutting process parameter when the dynamics model is formula (3) andthe cutting process model is formulas (4) and (6). The dynamics modelcan be expressed in a form represented in the following formula (8) bydeformation and time differentiation of formula (3).{umlaut over (f)} _(d)=2ζω_(n)({dot over (f)} _(c) −{dot over (f)}_(d))+ω_(n) ²(f _(c) −f _(d))  [Formula 8]ζ: equivalent damping coefficient,ω_(n): equivalent natural frequency

By substituting formula (4) that is the cutting process model intoformula (8) above, formula (9) below is obtained.

$\begin{matrix}{{{\overset{¨}{f}}_{d} = {{2{{ϛ\omega}_{n}\left( {{K^{c}{a\left( {{{\overset{.}{\overset{.}{h}}\left( {\varphi(t)} \right)}{g\left( {\varphi(t)} \right)}} + {{h\left( {\varphi(t)} \right)}{\overset{\_}{g}\left( {\varphi(t)} \right)}}} \right)}} - {\overset{.}{f}}_{d}} \right)}} + {\omega_{n}^{2}\left( {{K^{c}{{ah}\left( {\varphi(t)} \right)}{g\left( {\varphi(t)} \right)}} - f_{d}} \right)}}}\mspace{20mu}{{\overset{\_}{g}\left( {\varphi(t)} \right)} = \left\{ \begin{matrix}1 & \left( {{\varphi = \varphi_{s}},\varphi_{f}} \right) \\0 & ({otherwise})\end{matrix} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Further, when the right side of formula (9) is expressed by separatingit into known numbers and unknown numbers, formula (10) is obtained.

$\begin{matrix}{{\overset{¨}{f}}_{d} = {\left\lbrack {{a\left( {{{\overset{.}{h}\left( {\varphi(t)} \right)}{g\left( {\varphi(t)} \right)}} + {{h\left( {\varphi(t)} \right)}{\overset{\_}{g}\left( {\varphi(t)} \right)}}} \right)} - {{\overset{.}{f}}_{d}\mspace{14mu}{{ah}\left( {\varphi(t)} \right)}{g\left( {\varphi(t)} \right)}} - f_{d}} \right\rbrack\begin{bmatrix}{2{ϛ\omega}_{n}K^{c}} \\{2{ϛ\omega}_{n}} \\{\omega_{n}^{2}K^{c}} \\\omega_{n}^{2}\end{bmatrix}}} & \left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Formula (10) is an equation model for calculating a second derivative ofa disturbance force when the dynamic characteristic parameters and thecutting process parameters are provided. The identification unit 17substitutes the estimated disturbance force transformed into the toolreference coordinate system by the coordinate transformation unit 12into formula (10) to calculate the dynamic characteristic parameters andthe cutting process parameters satisfying formula (10). As an example,by arranging as many formulas (10) as n (n is an integer of one or more)points of time, they can be expressed in a matrix form of formula (11).The identification unit 17 can calculate the dynamic characteristicparameters and the cutting process parameters by applying the leastsquare method to formula (11).

$\begin{matrix}{\begin{bmatrix}{\overset{¨}{f}}_{d,1} \\\vdots \\{\overset{¨}{f}}_{d,n}\end{bmatrix} = {\left\lbrack \begin{matrix}{a\left( {{{\overset{.}{h}}_{1}g_{1}} + {h_{1}{\overset{\_}{g}}_{1}}} \right)} & {- {\overset{.}{f}}_{d,1}} & {{ah}_{1}g_{1}} & {- f_{d,1}} \\\vdots & \vdots & \vdots & \vdots \\{a\left( {{{\overset{.}{h}}_{n}g_{n}} + {h_{n}{\overset{\_}{g}}_{n}}} \right)} & {- {\overset{.}{f}}_{d,n}} & {{ah}_{n}g_{n}} & {- f_{d,n}}\end{matrix} \right\rbrack{\quad\begin{bmatrix}{2{ϛ\omega}_{n}K^{c}} \\{2{ϛ\omega}_{n}} \\{\omega_{n}^{2}K^{c}} \\\omega_{n}^{2}\end{bmatrix}}}} & \left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack\end{matrix}$

The above has described a method of deriving formula (10) and formula(11) from formula (9), and calculating the dynamic characteristicparameters and the cutting process parameters based on formula (10) orformula (11). Instead of formula (9), formula (12) may be used toperform the same calculation. In formula (12), a cutting determinationfunction g(φ(t)) in formula (9) is replaced with a differentiablefunction δ(φ(t)). δ(φ(t)) may be any differentiable function that canapproximate the cutting determination function g(φ(t)), and is notlimited to the form shown below.

$\begin{matrix}{{{\overset{¨}{f}}_{d} = {{2{{ϛ\omega}_{n}\left( {{K^{c}{a\left( {{{\overset{.}{h}\left( {\varphi(t)} \right)}{\delta\left( {\varphi(t)} \right)}} + {{h\left( {\varphi(t)} \right)}{\overset{.}{\delta}\left( {\varphi(t)} \right)}}} \right)}} - {\overset{.}{f}}_{d}} \right)}} + {\omega_{n}^{2}\left( {{K^{c}{{ah}\left( {\varphi(t)} \right)}{\delta\left( {\varphi(t)} \right)}} - f_{d}} \right)}}}\mspace{20mu}{{\delta\left( {\varphi(t)} \right)} = {{ϛ\left( {{\varphi(t)},\varphi_{s}} \right)} - {ϛ\left( {{\varphi(t)},\varphi_{f}} \right)}}}\mspace{20mu}{{ϛ\left( {x,y} \right)} = \frac{1}{1 + e^{- {b{({x - y})}}}}}} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack\end{matrix}$

As another example, by multiplying both sides of formula (10) or formula(11) by a smoothing window function, the dynamic characteristicparameters and the cutting process parameters can be calculated withoutbeing affected by differential errors.

As still another example, the identification unit 17 may perform arepeat operation using a search algorithm to search for the dynamiccharacteristic parameters and the cutting process parameters fromformula (10) or formula (11). The calculation of the dynamiccharacteristic parameters and the cutting process parameters in theidentification unit 17 is not limited to the operation using formula(10) and formula (11). By setting in advance an equation model of thedynamic characteristic parameters, the cutting process parameters, andthe disturbance force or disturbance torque according to the forms ofthe dynamics model and the cutting process model, the dynamiccharacteristic parameters and the cutting process parameters can becalculated from the equation model and the estimated disturbance forceor disturbance torque.

Further, identifiable parameters are not limited to the equivalentdamping coefficient, the equivalent natural frequency, and the specificcutting resistance. For example, by configuring a dynamics model thatincludes a vibration mode vector in the dynamic characteristicparameters, and setting an equation model of the dynamic characteristicparameters, the cutting process parameters, and the disturbance force,the identification unit 17 can identify the dynamic characteristicparameters including the vibration mode vector. As another example, byconfiguring a cutting process model that includes a tool eccentricity inthe cutting process parameters using formula (7), and setting anequation model of the dynamic characteristic parameters, the cuttingprocess parameters, and the disturbance force, the identification unit17 can identify the cutting process parameters.

As described above, the identification unit 17 calculates the cuttingprocess parameters that determine the characteristics of the cuttingprocess model and the dynamic characteristic parameters that determinethe characteristics of the dynamics model of the machine tool 2, usingthe disturbance force output from the coordinate transformation unit 12,the predetermined equation models, and the cutting conditions. The aboveequation models define the relationships between the cutting processparameters, the dynamic characteristic parameters, and the disturbanceforce.

Next, a hardware configuration of the numerical control system 1 will bedescribed. The command value generation unit 11, the coordinatetransformation unit 12, at least part of the machine drive control units13 and 15, the disturbance estimation units 14 and 16 and theidentification unit 17 illustrated in FIG. 1 are implemented by aprocessing circuit. The machine drive control units 13 and 15 mayinclude a circuit such as an inverter that generates motor current. Thestorage unit 18 is implemented by memory. The processing circuit may bea circuit including a processor, or may be dedicated hardware.

When the processing circuit is a circuit including a processor, theprocessing circuit is, for example, a processing circuit of aconfiguration illustrated in FIG. 9 . FIG. 9 is a diagram illustrating aconfiguration example of the processing circuit. A processing circuit200 includes a processor 201 and memory 202. When the command valuegeneration unit 11, the coordinate transformation unit 12, at least partof the machine drive control units 13 and 15, the disturbance estimationunits 14 and 16, and the identification unit 17 are implemented by theprocessing circuit 200 illustrated in FIG. 9 , these are implemented bythe processor 201 reading and executing programs stored in the memory202. That is, when the command value generation unit 11, the coordinatetransformation unit 12, at least part of the machine drive control units13 and 15, the disturbance estimation units 14 and 16, and theidentification unit 17 are implemented by the processing circuit 200illustrated in FIG. 9 , the functions of them are implemented usingprograms that are software. The memory 202 is also used as a work areaof the processor 201. The processor 201 is a Central Processing Unit(CPU) or the like. The memory 202 corresponds to nonvolatile or volatilesemiconductor memory such as Random Access Memory (RAM), Read OnlyMemory (ROM), or a flash memory, or a magnetic disk or the like. Thememory implementing the storage unit 18 may be the same as or differentfrom the memory 202.

When the processing circuit implementing the command value generationunit 11, the coordinate transformation unit 12, at least part of themachine drive control units 13 and 15, the disturbance estimation units14 and 16, and the identification unit 17 is dedicated hardware, theprocessing circuit is, for example, a Field Programmable Gate Array(FPGA), or an Application Specific Integrated Circuit (ASIC). Thecommand value generation unit 11, the coordinate transformation unit 12,at least part of the machine drive control units 13 and 15, thedisturbance estimation units 14 and 16, and the identification unit 17may be implemented by a combination of a processing circuit including aprocessor and dedicated hardware. The command value generation unit 11,the coordinate transformation unit 12, at least part of the machinedrive control units 13 and 15, the disturbance estimation units 14 and16, and the identification unit 17 may be implemented by a plurality ofprocessing circuits.

As described above, in the numerical control system 1 of the firstembodiment, the coordinate transformation unit 12 coordinate-transformsestimated disturbance forces calculated by the disturbance estimationunits 14 and 16 into the tool reference coordinate system, and theidentification unit 17 identifies the dynamic characteristic parametersand the cutting process parameters from the equation models of thedynamic characteristic parameters, the cutting process parameters, andthe disturbance force which is constructed based on the dynamics model,the cutting process model, and the cutting conditions. Thus, thenumerical control system 1 has an advantage of being able tosimultaneously calculate the dynamic characteristic parameters and thecutting process parameters that are cutting dominant parameters.

As a comparative example, consider an example of identifying cuttingprocess parameters, based on detection results of force sensors providedto machine drive systems and a cutting process model. Detection resultsof the force sensors are results of detection of forces caused by acutting force transmitted through mechanical structures, i.e.disturbance forces. Thus, the comparative example does not consider thata cutting force is transmitted as disturbance forces by mechanicaldynamics. Therefore, the comparative example cannot identify accuratecutting process parameters. By contrast, in the first embodiment, thedisturbance estimation units 14 and 16 estimate disturbance forces, andthe identification unit 17 identifies the dynamic characteristicparameters and the cutting process parameters from the equation modelsof the dynamic characteristic parameters, the cutting processparameters, and the disturbance force which is constructed based on thedynamics model, the cutting process model, and the cutting conditions.Therefore, the first embodiment can identify the cutting processparameters more accurately than the comparative example.

In the first embodiment, acceleration sensors are provided to allmachine drive systems including a spindle drive system and a feed drivesystem. However, the number of machine drive systems at whichacceleration sensors are installed is not limited to the total number ofmachine drive systems. For example, acceleration sensors may be providedto three linear feed drive systems without providing an accelerationsensor to a spindle drive system, and a disturbance force vector may becalculated from results of detection by the acceleration sensors of thethree linear feed drive systems. Alternatively, acceleration sensors maybe provided to two linear feed drive systems without providing anacceleration sensor to a spindle drive system, and a two-dimensionaldisturbance force vector on a plane formed by the feed drive systems maybe calculated from results of detection by the acceleration sensors toestimate dynamic characteristic parameters and cutting processparameters on the plane. Alternatively, a two-dimensional disturbanceforce vector on a plane perpendicular to a spindle drive system may becalculated from a result of detection by an acceleration sensor providedto the spindle drive system, and a disturbance force in the direction ofa feed drive system parallel to the spindle drive system may be addedthereto from a detection result of an acceleration sensor provided tothe feed drive system, to calculate a three-dimensional disturbanceforce vector.

Further, the first embodiment has described a configuration for amachine tool having three linear feed drive systems and a spindle drivesystem, but the present invention is not limited to machine tools ofthis shaft configuration. For example, when a machine tool includes oneor more rotating feed drive systems in addition to three linear feeddrive systems and a spindle drive system, effects equivalent to those ofthe first embodiment can be achieved by the following configuration.Specifically, the command value generation unit 11 outputs a toolrelative attitude in the NC program coordinate system to the coordinatetransformation unit 12, and the coordinate transformation unit 12coordinate-transforms a disturbance force acting on the feed drivesystem and a disturbance force acting on the spindle drive system intothe tool reference coordinate system, taking the relative attitude ofthe tool into account, so that an estimated disturbance force vector canbe calculated as in the first embodiment.

Furthermore, in the first embodiment, acceleration sensors are used asmeans for detecting the acceleration of machine drive systems, butphysical quantities to be detected are not limited to acceleration.Sensors that directly detect velocity such as velocity sensors, gyrosensors, or laser Doppler meters may be used. That is, using sensorsthat can detect a physical quantity obtained by first or higher ordertime differentiation of the amount of displacement does not depart fromthe gist of the present invention.

Moreover, the numerical control system 1 described in the firstembodiment may be composed of a plurality of devices. For example, themotor drive controller 100 including the machine drive control units 13and 15 and the disturbance estimation units 14 and 16, and the othercomponents of the numerical control system 1 may be formed as separatedevices. The numerical control system 1 may consist of a numericalcontrol device including the command value generation unit 11, themachine drive control units 13 and 15, the disturbance estimation units14 and 16, and the coordinate transformation unit 12, and an industrialcomputer including the identification unit 17 and the storage unit 18.The industrial computer may be installed in the vicinity of the machinetool 2, or may be installed in a place away from the machine tool 2. Theindustrial computer may be connected to a plurality of machine tools 2.The industrial computer may be connected to the outside through a publicline such as a wired or wireless Internet connection. When the numericalcontrol system 1 consists of a plurality of devices, the command valuegeneration unit 11, the coordinate transformation unit 12, at least partof the machine drive control units 13 and 15, the disturbance estimationunits 14 and 16, and the identification unit 17 are implemented byprocessing circuits mounted on devices on which they are mounted. Theseprocessing circuits may each be a processing circuit including aprocessor, dedicated hardware, or a combination of a processing circuitincluding a processor and dedicated hardware, like the processingcircuit described above.

In the first embodiment, a machine tool that performs milling byrotation of a tool has been described. The present invention is alsoapplicable to a machine tool that performs turning by rotation of aworkpiece.

Second Embodiment

FIG. 10 is a diagram illustrating a configuration example of a numericalcontrol system 1 a according to a second embodiment of the presentinvention. The numerical control system 1 a of the second embodimentcontrols a machine tool 2 a.

The machine tool 2 a includes a machine drive system 21 a as a feeddrive system and a machine drive system 22 a as a spindle drive system.The machine drive system 21 a and the machine drive system 22 a are thesame as the machine drive system 21 and the machine drive system 22 ofthe first embodiment, respectively, except that each is not providedwith an acceleration sensor. A force sensor 23 is provided to themachine tool 2 a. The force sensor 23 is installed, for example, on thetable 31 or inside the table 31 illustrated in FIG. 4 . The installationlocation of the force sensor 23 is not limited to this example. Theforce sensor 23 may be installed in any location in which it can detectforces applied to the machine drive systems. The force sensor 23 is anexample of a sensor that detects forces or torques applied to themachine drive systems 21 a and 22 a.

In the first embodiment, disturbance forces are estimated using resultsdetected by acceleration sensors, encoder signals, and motor currentsignals. In the second embodiment, using the force sensor 23 eliminatesthe need to provide the disturbance estimation units 14 and 16 to thenumerical control system 1 a. The numerical control system 1 a of thesecond embodiment is configured by removing the disturbance estimationunits 14 and 16 from the numerical control system 1 of the firstembodiment, and results of detection by the force sensor 23 are input tothe coordinate transformation unit 12. The same reference numerals asthose in the first embodiment are assigned to components having the samefunctions as those of the first embodiment without duplicatedexplanations. Hereinafter, differences from the first embodiment will bedescribed.

The coordinate transformation unit 12 performs coordinate transformationas in the first embodiment, using results of detection by the forcesensor 23 instead of a disturbance force acting on the feed drive systemand a disturbance force acting on the spindle drive system input fromthe disturbance estimation units 14 and 16, respectively, and outputs acoordinate-transformed disturbance force to the identification unit 17like the estimated disturbance force in the first embodiment. That is,in the second embodiment, the coordinate transformation unit 12 acquiresdisturbance forces from detection results detected by a sensor thatdetects forces or torques applied to the machine drive systems 21 a and22 a. When this sensor is a sensor detecting torques, the coordinatetransformation unit 12 performs coordinate transformation afterconverting the torques into forces. The identification unit 17calculates the dynamic characteristic parameters and the cutting processparameters as in the first embodiment. The operation of the numericalcontrol system 1 a other than that described above is the same as theoperation of the numerical control system 1 of the first embodiment. Thecoordinate transformation unit 12 may coordinate-transform a detectedtorque and output it to the identification unit 17, and theidentification unit 17 may calculate the dynamic characteristicparameters and the cutting process parameters using thecoordinate-transformed torque.

As described above, in the second embodiment, using the force sensor 23without using the acceleration sensors and the disturbance estimationunits 14 and 16, the dynamic characteristic parameters and the cuttingprocess parameters can be calculated as in the first embodiment. Thus,the second embodiment has the same effects as the first embodiment.

Third Embodiment

FIG. 11 is a block diagram illustrating a configuration example of adisturbance estimation unit according to a third embodiment of thepresent invention. A numerical control system of the third embodiment isthe same as the numerical control system 1 of the first embodimentexcept that it includes a disturbance estimation unit 14 a instead ofthe disturbance estimation unit 14 of the first embodiment. Hereinafter,differences from the first embodiment will be described.

The disturbance estimation unit 14 of the first embodiment acquires amachine drive system signal and an acceleration sensor signal from themachine drive system 21 modeled as a single inertia system, to calculatea disturbance force in a high-frequency band that cannot be estimatedonly with the signal within machine drive system, with the aid of theacceleration sensor. A machine drive system of a machine tool isgenerally formed as a structure having a plurality of inertias such as amotor, a ball screw, and a table.

FIG. 12 is a diagram illustrating an example of a model of the machinedrive system 21. FIG. 12 illustrates an example of a model of themachine drive system 21 modeled as a three-inertia system correspondingto a motor as a servomotor, a ball screw, and a table when the machinedrive system 21 includes the servomotor, the ball screw, and the table.T_(m) denotes a motor torque, θ_(m) denotes a motor angle, J_(m) andJ_(b) denote inertias, M_(t) denotes a mass, D_(m), D_(b), and C_(t)denote damping coefficients, K_(g) and K_(t) denote spring constants, Rdenotes a ball screw pitch, and x_(t) denotes a position. Here, m, b,and t are subscripts indicating the motor, the ball screw, and thetable, respectively.

Because the machine drive system 21 generally has a structure having aplurality of inertias as described above, it is desirable to divide thestructure into a plurality of segments for modeling to accurately modelthe behavior of the structure. Therefore, the disturbance estimationunit 14 a of the third embodiment divides the structure into a pluralityof segments for modeling, divides an acceleration sensor signal outputfrom the acceleration sensor 211 according to frequency bands, andestimates a disturbance force using inverse models according to thebands.

Here, as illustrated in FIG. 11 , the machine drive system 21 is dividedinto a first structure 213 and a second structure 212 for modeling. Thatis, the machine drive system 21 includes the first structure 213 and thesecond structure 212 including the motor. The disturbance estimationunit 14 a calculates an actual power of machine drive system that is theresultant of forces applied to the first structure 213, based on aplurality of first structure models of the first structure 213 and theacceleration sensor signal. The disturbance estimation unit 14 a alsocalculates a power command of machine drive system that is a forceapplied by the motor to the machine drive system, based on a secondstructure model of the second structure 212, a detection result of amotor current flowing through the motor, and a detection result of theposition of the motor. Then, the disturbance estimation unit 14 aestimates a disturbance force using the actual power of machine drivesystem and the command power of machine drive system. The plurality offirst structure models have different frequency characteristicsdetermined according to the divided frequency bands.

In the machine drive system 21 in FIG. 11 , equivalent models of thefirst structure 213 and the second structure 212 are illustrated.I_(ref) denotes a motor current, K denotes a torque constant, v_(t)denotes a table velocity, and F_(d) denotes a disturbance force. a_(t)^(exp) is an acceleration sensor signal output from the accelerationsensor 211. The subscript ref indicates that it is a reference valuecalculated by the machine drive control unit 13, and the superscript expindicates that it is a signal directly detected by the accelerationsensor. The other characters have the same definitions as those in FIG.12 . The first structure is provided with the acceleration sensor 211.Here, the first structure is, for example, the table, and the secondstructure 212 is, for example, a mechanical structure in which theservomotor and the ball screw are combined. To the machine drive system21, a disturbance force is applied from the outside to the firststructure 213. Further, a command power of machine drive systemresulting from a torque output of the servomotor is applied to the firststructure 213, so that the position of the first structure 213 isindirectly controlled by the machine drive control unit 13.

The disturbance estimation unit 14 a illustrated in FIG. 11 estimates adisturbance force applied to the machine drive system 21 as an estimateddisturbance force acting on the feed drive system, based on an encodersignal and a motor current signal output from the machine drive system21 and an acceleration sensor signal output from the acceleration sensor211.

Specifically, the disturbance estimation unit 14 a includes firststructure model units 143 and 144 corresponding to the first structure213, a second structure model unit 141 corresponding to the secondstructure, and a synthesis unit 142. In the disturbance estimation unit14 a in FIG. 11 , inverse models of the corresponding structures of theunits are illustrated. LPF indicates a low-pass filter, and HPFindicates a high-pass filter. Characters with a hat above indicateestimated values.

The first structure model unit 143 and the first structure model unit144 each calculate an actual power of machine drive system that is aforce applied to the first structure 213, based on the accelerationsensor signal. The first structure model unit 143 includes the low-passfilter, and the first structure model unit 144 includes the high-passfilter. These filters serve to separate the acceleration sensor signalinto a first frequency band and a second frequency band at apredetermined cutoff frequency. Here, the cut-off frequency of thelow-pass filter and the high-pass filter is a frequency upper limit atwhich the machine drive control unit 13 can control the machine drivesystem 21, for example. The acceleration sensor signal separated intothe two bands passes through the first structure model unit 143 and thefirst structure model unit 144, so that the first structure model unit143 outputs a first actual power of machine drive system that is anactual power of machine drive system on the low frequency side, and thefirst structure model unit 144 outputs a second actual power of machinedrive system that is an actual power of machine drive system on the highfrequency side.

The second structure model unit 141 calculates a command power ofmachine drive system that is a drive force for the motor to operate themachine drive system 21, using the motor current signal and the encodersignal. The synthesis unit 142 calculates the sum of the first actualpower of machine drive system and the second actual power of machinedrive system, and subtracts the command power of machine drive systemfrom the calculated sum, thereby being able to estimate a disturbanceforce F_(d) applied to the machine drive system 21.

In the example illustrated in FIG. 11 , the machine drive system 21 isexpressed as a model composed of three inertias, spring elements thatcouple the inertias, and damper elements that represent viscousfriction. The model of the machine drive system 21 is not limited tothis. The machine drive system 21 may be expressed as a model that takesdead time due to communication of the encoder or the acceleration sensorand Coulomb friction into account. In this case, two first structuremodel units and a single second structure model unit corresponding tothem may be included in the disturbance estimation unit 14 a.

Parameters included in the inverse models used by the disturbanceestimation unit 14 a can be calculated by a method described below. Forexample, the machine drive control unit 13 provides an impulseexcitation command, a random excitation command, or a sine sweepexcitation command to the motor of the machine drive system 21. Theparameters can be fitted based on frequency response obtained from anencoder signal and an acceleration sensor signal at this time. Asanother example, instead of using the servomotor as an excitationsource, the feed drive system may be excited from the outside using animpulse hammer, to fit parameters. As still another example, testmachining that produces a disturbance force known in advance may beperformed, and the parameters may be fitted using a motor currentsignal, an encoder signal, and an acceleration sensor signal output atthis time. As still another example, the parameters may be calculatedusing finite element analysis. Further, the parameters may be determinedby a combination of those described above.

Here, the effects of the third embodiment will be described. FIG. 13 isa diagram illustrating disturbance force estimation results in acomparative example. In the comparative example whose estimation resultsare illustrated in FIG. 13 , as in the technique according to the thirdembodiment, the state quantity of the motor and the ball screw, i.e. thefirst structure is estimated using the motor current signal and theencoder signal, the state quantity of the table is estimated using theacceleration sensor signal, and the disturbance is estimated using theseestimation results. The difference between the third embodiment and thecomparative example is that the comparative example does not include aplurality of first structure model units as in FIG. 11 , but includes asingle first structure model unit. That is, in the technique of thecomparative example, the mass of the table provided with theacceleration sensor is not decomposed according to frequency bands. Inan upper row of FIG. 13 , an actual disturbance force, that is, adisturbance force actually measured using a force sensor is illustrated,and in a lower row of FIG. 13 , results estimated by the comparativeexample are illustrated. As can be seen from FIG. 13 , in thecomparative example, estimate values do not coincide with valuesactually measured by the force sensor in a high frequency band. That is,the technique of the comparative example, which does not decompose themass of the table provided with the acceleration sensor according tofrequency bands for a multi-inertia drive system typified by a ballscrew drive, cannot accurately estimate the disturbance force.

By contrast, in the third embodiment, an acceleration sensor signal isdivided according to frequency bands, and different inverse models areprovided to the different bands to estimate a disturbance force. FIG. 14is a diagram illustrating an example of a disturbance force estimated bythe disturbance estimation unit 14 a of the third embodiment. In anupper row of FIG. 14 , an actual disturbance force, that is, adisturbance force actually measured using a force sensor is illustrated,and in a lower row of FIG. 14 , results estimated by the disturbanceestimation unit 14 a of the third embodiment are illustrated. As can beseen from FIG. 14 , by using the disturbance estimation unit 14 a of thethird embodiment, the estimation results equivalent to the results ofmeasurement by the force sensor can be obtained. That is, thedisturbance estimation unit 14 a of the third embodiment has anadvantage of being able to accurately estimate a disturbance forceapplied to a machine drive system in a machine tool including amulti-inertia drive system typified by a ball screw drive.

In the above description, the acceleration sensor is used as a means fordetecting the acceleration of the machine drive system 21, but thephysical quantity to be detected is not limited to acceleration. Sensorsthat directly detect speed such as speed sensors, gyro sensors, or laserDoppler meters may be used. That is, using sensors that can detect aphysical quantity obtained by first or higher order time differentiationof the amount of displacement does not depart from the gist of thepresent invention.

Although in the third embodiment, the ball screw drive machine tool hasbeen described, the disturbance force estimation technique described inthe third embodiment is not limited to ball screw drive machine tools.The technique is also applicable to a feed drive system and a spindledrive system driven by a means other than a ball screw as long as theyare machine drive systems that can be modeled as a multi-inertia system,that is, machine drive systems composed of a plurality of inertialbodies.

In the third embodiment, the two first structure models are provided inthe disturbance estimation unit 14 a to divide the frequency band intotwo bands, but the number of first structure models and the number offilters are not limited to two. For example, three or more firststructure models may be provided, and their filters may be designed todivide the frequency band into the same number of bands as the number offirst structure models.

In the above description, the example of using the disturbanceestimation unit 14 a instead of the disturbance estimation unit 14 ofthe numerical control system 1 of the first embodiment has beendescribed. However, when the motor drive controller 100 illustrated inFIG. 1 is provided singly, the disturbance estimation unit 14 a may beused instead of the disturbance estimation unit 14.

Fourth Embodiment

FIG. 15 is a block diagram illustrating a configuration example of adisturbance estimation unit according to a fourth embodiment of thepresent invention. A numerical control system of the fourth embodimentis the same as the numerical control system 1 of the first embodimentexcept that it includes a disturbance estimation unit 14 b instead ofthe disturbance estimation unit 14 of the first embodiment. Hereinafter,differences from the first embodiment will be described.

The disturbance estimation unit 14 a of the third embodiment divides anacceleration sensor signal according to frequency bands, and providesdifferent inverse models to the different bands to estimate adisturbance force. The disturbance estimation unit 14 b of the fourthembodiment uses a model in which a table provided with an accelerationsensor is divided into a first table inertia that is estimated using anencoder signal and a motor current signal and a second table inertiathat is estimated using an acceleration sensor signal, to estimate adisturbance force. FIG. 16 is a diagram illustrating an example ofmodeling of the machine drive system 21 in the fourth embodiment.Characters in FIG. 16 are the same as those in the third embodiment.Note that those with a subscript including 1 correspond to a first tableinertia model, and those with a subscript including 2 correspond to asecond table inertia model.

Specifically, the disturbance estimation unit 14 b calculates an actualpower of machine drive system corresponding to a first structure modelof the machine drive system 21 based on the first structure model andthe acceleration sensor signal. The disturbance estimation unit 14 balso calculates a command power of machine drive system that is a forceapplied by the motor to the machine drive system 21, based on a secondstructure model of the machine drive system 21 including the motor ofthe machine drive system 21, a detection result of a motor currentflowing through the motor, and a detection result of the position of themotor. The disturbance estimation unit 14 b estimates a disturbanceforce using the actual power of machine drive system and the commandpower of machine drive system. One of a plurality of structuresconstituting the machine drive system is divided into a first inertialbody model and a second inertial body model for modeling. The secondstructure model includes the first inertial body model, and the secondstructure model includes the second inertial body model. An example ofthe first inertial body model and the second inertial body model is thefirst table inertia model and the second table inertia model describedabove.

The definitions of characters in FIG. 15 are the same as those in thethird embodiment. The machine drive system 21 includes a table, aservomotor, and a ball screw as in the third embodiment. In the fourthembodiment, the model of the table is divided into two models which area first table inertia and a second table inertia, and modeling isperformed with a first structure 213 a that is regarded as the table,and a second structure 212 a that is regarded as a mechanical structurein which the table, the motor, and the ball screw are combined.

The disturbance estimation unit 14 b estimates a disturbance forceapplied to the machine drive system 21 as a disturbance force acting onthe feed drive system on the basis of an encoder signal and a motorcurrent signal output from the machine drive system 21, an accelerationsensor signal output from the acceleration sensor 211.

To the machine drive system 21, a disturbance force is applied from theoutside to the first structure 213 a. Further, a command power ofmachine drive system resulting from a torque output of the servomotor isapplied to the first structure 213 a, so that the position of the firststructure 213 a is indirectly controlled by the machine drive controlunit 13.

The disturbance estimation unit 14 b includes a first structure modelunit 143 a corresponding to the first structure 213 a, a secondstructure model unit 141 a corresponding to the second structure 212 a,and a synthesis unit 142 a. The first structure model unit 143 acalculates an actual power of machine drive system that is the resultantof forces applied to the first structure 213 a, based on theacceleration sensor signal. The first structure model unit 143 aincludes an LPF for noise reduction.

The second structure model unit 141 a calculates a command power ofmachine drive system that is a drive force for the motor to operate themachine drive system 21, using the motor current signal and the encodersignal. Here, unlike the second structure 212 in the third embodiment,the model of the second structure 212 a is a model including the secondtable inertia that is a division of the inertia of the table. Thesynthesis unit 142 a can estimate a disturbance force F_(d) applied tothe machine drive system by adding up the actual power of machine drivesystem and the command power of machine drive system.

A method of calculating parameters included in inverse models used inthe disturbance estimation unit 14 b is the same as the method ofcalculating the parameters included in the inverse models used in thedisturbance estimation unit 14 a of the third embodiment.

As described above, the disturbance estimation unit 14 b of the fourthembodiment estimates a disturbance force, using the models obtained bydividing the table into the first table inertia that is estimated usingthe machine drive system signal and the second table inertia that isestimated using the acceleration sensor signal. By thus dividing astructure provided with an acceleration sensor of the structuresconstituting the machine drive system 21 into two segments for modeling,the same effects as those of the first embodiment can be achieved, and adisturbance force can be accurately estimated.

In the above description, the example of using the disturbanceestimation unit 14 b instead of the disturbance estimation unit 14 ofthe numerical control system 1 of the first embodiment has beendescribed. When the motor drive controller 100 illustrated in FIG. 1 isprovided singly, the disturbance estimation unit 14 b may be usedinstead of the disturbance estimation unit 14.

Fifth Embodiment

FIG. 17 is a block diagram illustrating a configuration example of adisturbance estimation unit according to a fifth embodiment of thepresent invention. A numerical control system of the fifth embodiment isthe same as the numerical control system 1 of the first embodimentexcept that it includes a disturbance estimation unit 14 c instead ofthe disturbance estimation unit 14 of the first embodiment. Hereinafter,differences from the first embodiment will be described.

The first, third, and fourth embodiments are configured to estimate adisturbance force by the combined use of the encoder signal, the motorcurrent signal, and the acceleration sensor signal. The motor currentsignal, the encoder signal, and the acceleration sensor signal aresignals generated from different signal sources. Thus, the times atwhich the disturbance estimation unit acquires the signals are notnecessarily synchronized, and synchronization errors generally occur.Therefore, as illustrated in FIG. 17 , the disturbance estimation unit14 c of the fifth embodiment has a configuration in which a signalsynchronization unit 145 is added to the disturbance estimation unit 14b described in the fourth embodiment.

In the signal synchronization unit 145, a first correction time ispreset for the encoder signal and a second correction time is preset forthe acceleration sensor signal. The first correction time is a time lagof the encoder signal with respect to the motor current signal. Thesecond correction time is a time lag of the acceleration sensor signalwith respect to the motor current signal. Further, the signalsynchronization unit 145 can record the encoder signal corresponding tothe first correction time and the acceleration sensor signalcorresponding to the second correction time. When the motor currentsignal is input at a certain time, the signal synchronization unit 145outputs the encoder signal at a time different from the certain time bythe first correction time and the acceleration sensor signal at a timedifferent from the certain time by the second correction time togetherwith the motor current signal. If sampling rates of the motor currentsignal, the encoder signal, and the acceleration sensor signal aredifferent from each other, the encoder signal and the accelerationsensor signal at times different from the certain time by the first andsecond correction times, respectively, can be calculated by timeinterpolation or extrapolation. As described above, the disturbanceestimation unit 14 c corrects the time lags produced between the motorcurrent signal, the encoder signal, and the acceleration sensor signal,and estimates the disturbance force using the signals corrected in thetime lags. Here, a method of synchronizing the times of the encodersignal and the acceleration sensor signal with the motor current signalhas been described. Alternatively, the signals may be synchronized withrespect to one of the encoder signal and the acceleration sensor signal.Alternatively, a reference trigger signal for synchronization may begenerated in the signal synchronization unit 145, and the signals may besynchronized based on the reference trigger signal.

As described above, the disturbance estimation unit 14 c of the fifthembodiment is provided with the signal synchronization unit 145 tocorrect time synchronization errors between the signals, and thus canreduce time synchronization errors and can accurately estimate thedisturbance force.

In the example described above, the signal synchronization unit 145 isadded to the disturbance estimation unit 14 b of the fourth embodiment.Likewise, by adding the signal synchronization unit 145 to thedisturbance estimation unit 14 of the first embodiment and thedisturbance estimation unit 14 a of the third embodiment, timesynchronization errors can be corrected likewise.

Sixth Embodiment

FIG. 18 is a block diagram illustrating a configuration example of anumerical control system according to a sixth embodiment of the presentinvention. In a numerical control system 1 b of the sixth embodiment, asimulation unit 19 is added to the numerical control system 1 of thefirst embodiment, and a command value generation unit 11 a and anidentification unit 17 a are provided in place of the command valuegeneration unit 11 and the identification unit 17. Except for these, thenumerical control system 1 b of the sixth embodiment is the same as thenumerical control system 1 of the first embodiment. The same referencenumerals as those in the first embodiment are assigned to componentshaving the same functions as those of the first embodiment withoutduplicated explanations. Hereinafter, differences from the firstembodiment will be mainly described.

In the sixth embodiment, in the NC program, an identification command isdescribed in addition to the relative tool position command or the feeddrive system position command in the NC program coordinate system, thespindle drive system rotation command, and the feed rate command. Here,the identification command is a command for causing the identificationunit 17 a to start identification processing on the dynamiccharacteristic parameters and the cutting process parameters.

The command value generation unit 11 a analyzes commands described inthe NC program, generates machine drive system commands for the machinedrive systems 21 and 22 as in the first embodiment, and outputs them tothe corresponding machine drive control units 13 and 15. When theanalyzed commands include the identification command, the command valuegeneration unit 11 a outputs the identification command to theidentification unit 17 a. That is, when the NC program includes acommand that instructs execution of identification by the identificationunit 17 a, the command value generation unit 11 a instructs theidentification unit 17 a to calculate the cutting process parameters andthe dynamic characteristic parameters. Further, the command valuegeneration unit 11 a corrects the machine drive system commandsaccording to simulation results of the mechanical dynamics and thecutting process described below output from the simulation unit 19.

When the identification command output from the command value generationunit 11 a is input, the identification unit 17 a calculates the dynamiccharacteristic parameters and the cutting process parameters by the samemethod as the method described in the first embodiment, and outputs thecalculated results to the simulation unit 19. Further, theidentification unit 17 a compares an estimated disturbance force outputby the coordinate transformation unit 12 with a simulated disturbanceforce output by the simulation unit 19. Here, the estimated disturbanceforce is a cutting force calculated by the disturbance estimation unitsand coordinate-transformed by the coordinate transformation unit, andthe simulated disturbance force is a cutting force calculated by thesimulation unit 19. If the difference between the estimated disturbanceforce and the simulated disturbance force is larger than a threshold,the identification unit 17 a determines that the machining state haschanged, and executes the identification processing again. That is, theidentification unit 17 a calculates the difference between a disturbanceforce output from the coordinate transformation unit 12 and adisturbance force simulated by the simulation unit 19. When thedifference is larger than the threshold, the identification unit 17 acalculates the cutting process parameters and the dynamic characteristicparameters. When the estimated disturbance force and the simulateddisturbance force are calculated as vectors, the identification unit 17a can calculate the difference between the estimated disturbance forceand the simulated disturbance force by calculating norms for theirrespective cutting forces and comparing the norms. As another example,the identification unit 17 a may calculate the difference between theestimated disturbance force and the simulated disturbance force in acertain direction such as a tool traveling direction, and compare thedifference with the threshold.

The simulation unit 19 calculates machine drive system positions basedon encoder signals output from the machine drive systems 21 and 22, andsimulates vibrations of the structures around the tool and the workpieceand the cutting process between the tool and the workpiece, using thedynamics model, the cutting process model, and the cutting conditions.

Vibrations of the structures around the tool and the workpiece aresimulated as follows. Using the dynamics model, the simulation unit 19calculates, for one or both of the workpiece-side structure and thetool-side structure, relative displacements produced in the structureswhich are produced when a cutting force acts on them. The simulationunit 19 calculates a position deviation of the tool from the calculatedrelative displacements in the structures and the positions of themachine drive systems 21 and 22, and calculates disturbance forcesapplied to the machine drive systems 21 and 22. Here, the positiondeviation of the tool is the difference between a tool position when nocutting force is produced at the tool and a tool position when a cuttingforce is produced at the tool.

The cutting process is simulated as follows. The simulation unit 19calculates a trajectory of a tool tooth edge from the position deviationof the tool with respect to the workpiece and the tool rotation angle,using the cutting conditions and the cutting process model. Thesimulation unit 19 calculates an uncut chip thickness from thetrajectory of the tool tooth edge, and calculates a cutting forcecorresponding to the uncut chip thickness. The cutting force calculatedhere is output to the identification unit 17 a.

As described above, a cutting force used in the dynamics model iscalculated using the cutting process model, and a position deviation ofthe tool used in the cutting process is calculated using the dynamicsmodel. Thus, by alternately repeating the calculation using the dynamicsmodel and the calculation using the cutting process model, thesimulation unit 19 can simultaneously simulate the mechanical dynamicsand the cutting process from moment to moment. In other words, thesimulation unit 19 can simulate the cutting force produced between thetool and the workpiece, based on the motor current signal, the encodersignal, the cutting conditions, and the cutting process model, andsimulate the disturbance forces produced at the machine drive systemsand the relative position deviations of the tool and the workpiece whenthe cutting force is produced, based on the dynamics model.

Here, correction processing executed by the command value generationunit 11 a based on the results of simulation of the mechanical dynamicsand the cutting process performed by the simulation unit 19 will bedescribed. Using the position deviation of the tool simulated by thesimulation unit 19, the command value generation unit 11 a adds amovement amount corresponding to the deviation to the machine drivesystem commands for the feed drive systems. By this correction,dimensional errors caused by the position deviation of the tool can bereduced.

As another correction method, the command value generation unit 11 a maycompare thicknesses cut by the tool tooth edges simulated by thesimulation unit 19, and correct the feedrate per tooth or the feed drivesystem positions so that the maximum uncut chip thicknesses produced bythe tooth edges become equal. By this correction, vibrations of the tooltooth edges caused by changes in uncut chip thickness can be reduced. Asanother correction method, the command value generation unit 11 a maycalculate the maximum value or the mean value within a fixed time, usingcutting forces simulated by the simulation unit 19, and reduce thefeedrate per tooth when the calculation result exceeds a predeterminedcutting force upper limit. By this correction, the cutting force can belimited to the cutting force upper limit or lower. Tool breakage due toan excessive cutting force can be avoided.

As still another correction method, the command value generation unit 11a may compare cutting forces produced by the tooth edges during onerotation of the tool, using cutting forces simulated by the simulationunit 19, and correct the feedrate per tooth or the spindle drive systemrotation speed so that the maximum values of cutting forces produced bythe tooth edges become equal. By this correction, a cutting forceapplied to a certain tooth edge is reduced, so that cutting forces canbe produced equally for the tooth edges.

As still another correction method, the command value generation unit 11a may calculate machined surface roughness from a trajectory of a tooltooth edge simulated by the simulation unit 19, and reduce the feedrateper tooth when the machined surface roughness exceeds a predeterminedmachined surface roughness upper limit. By this correction, a finishedsurface with machined surface roughness lower than or equal to themachined surface roughness upper limit is formed. A plurality ofprocesses of the above-described correction processes may be combined.

As described above, the numerical control system 1 b of the sixthembodiment identifies the dynamic characteristic parameters and thecutting process parameters at a timing described in the NC program or atiming when it is determined that the machining state has changed, andfurther simulates the mechanical dynamics and the cutting process, andcorrects by the command value generation unit the machine drive systemcommands based on the simulation results. Thus, the following effectsare achieved.

Because the identification unit 17 a executes processing upon receptionof the identification command, the numerical control system 1 b canidentify the dynamic characteristic parameters and the cutting processparameters at a timing specified by the NC program. Therefore, even ifthe machining state changes during the same NC program, the dynamiccharacteristic parameters and the cutting process parameters can beidentified at a timing described in the NC program.

Further, the identification unit 17 a compares an estimated disturbanceforce with a simulated disturbance force, so that the dynamiccharacteristic parameters and the cutting process parameters thatdetermine the characteristics of the dynamics model and the cuttingprocess model can be verified. Therefore, when the mechanical dynamicsor the cutting process has changed, the identification processing can beexecuted so that the simulation unit can correctly simulate thedisturbance force compared to the estimated disturbance force.Furthermore, the simulation unit 19 simulates the mechanical dynamicsand the cutting process, so that the cutting process can be changed inreal time.

Thus, the numerical control system 1 b described in the sixth embodimentcan execute the identification processing at a timing not specified inthe NC program when the mechanical dynamics or the cutting process haschanged, in addition to the timing specified in the NC program. Byexecuting a simulation using the dynamics model and the cutting processmodel whose characteristics have been determined by the dynamiccharacteristic parameters and the cutting process parameters obtainedfrom the identification processing, the command value generation unitcan make corrections based on the simulation results to the machinedrive systems.

FIG. 19 is a block diagram illustrating another configuration example ofthe numerical control system of the sixth embodiment. In the exampleillustrated in FIG. 18 , feedback positions indicated by encoder signalsthat can be acquired from the machine drive systems 21 and 22 are inputto the simulation unit 19. In the configuration example illustrated inFIG. 19 , instead of the feedback positions, command positions generatedin the machine drive control units 13 and 15 are input to the simulationunit 19. The simulation unit 19 performs a simulation like thesimulation unit 19 in the configuration example illustrated in FIG. 18 ,using the command positions generated in the machine drive control units13 and 15, instead of the feedback positions. The operation in theconfiguration example illustrated in FIG. 19 is the same as theoperation in the configuration example illustrated in FIG. 18 except forthe point described above. In FIG. 19 , the same reference numerals areassigned to components having the functions illustrated in FIG. 18 . Theconfiguration illustrated in FIG. 19 can achieve effects equivalent tothose of the numerical control system 1 b illustrated in FIG. 18 .

Seventh Embodiment

FIG. 20 is a block diagram illustrating a configuration example of anumerical control system according to a seventh embodiment of thepresent invention. A numerical control system 1 c of the seventhembodiment is configured by adding a simulation unit 19 to the numericalcontrol system 1 a of the second embodiment. Except for these, thenumerical control system 1 c of the seventh embodiment is the same asthe numerical control system 1 a of the second embodiment. The samereference numerals as those in the second embodiment are assigned tocomponents having the same functions as those of the second and sixthembodiments without duplicated explanations.

Thus, in the seventh embodiment, the dynamic characteristic parametersand the cutting process parameters are calculated as in the firstembodiment, using the force sensor 23 without using the accelerationsensors and the disturbance estimation units 14 and 16. Further, thedynamic characteristic parameters and the cutting process parameters areidentified at a timing described in the NC program or a timing when itis determined that the machining state has changed. Furthermore, themechanical dynamics and the cutting process are simulated, and thecommand value generation unit corrects machine drive system commandsbased on the simulation results. Thus, the seventh embodiment has thesame effects as the sixth embodiment.

FIG. 21 is a block diagram illustrating another configuration example ofthe numerical control system of the seventh embodiment. In the exampleillustrated in FIG. 20 , feedback positions indicated by encoder signalsthat can be acquired from the machine drive systems 21 a and 22 a areinput to the simulation unit 19. In the configuration exampleillustrated in FIG. 21 , instead of the feedback positions, commandpositions generated in the machine drive control units 13 and 15 areinput to the simulation unit 19. The simulation unit 19 performs asimulation like the simulation unit 19 in the configuration exampleillustrated in FIG. 20 , using the command positions generated in themachine drive control units 13 and 15, instead of the feedbackpositions. The operation in the configuration example illustrated inFIG. 21 is the same as the operation in the configuration exampleillustrated in FIG. 20 except for the point described above. In FIG. 21, the same reference numerals are assigned to components having thefunctions illustrated in FIG. 20 . The configuration illustrated in FIG.21 can achieve effects equivalent to those of the numerical controlsystem 1 c illustrated in FIG. 20 .

The configurations described in the above embodiments illustrate anexample of the subject matter of the present invention, and can becombined with another known art, and can be partly omitted or changedwithout departing from the scope of the present invention.

REFERENCE SIGNS LIST

1, 1 a, 1 b, 1 c numerical control system; 2, 2 a machine tool; 11, 11 acommand value generation unit; 12 coordinate transformation unit; 13, 15machine drive control unit; 14, 14 a, 14 b, 14 c, 16 disturbanceestimation unit; 17, 17 a identification unit; 18 storage unit; 21, 21a, 22, 22 a machine drive system; 23 force sensor; 31 table; 32workpiece; 33 tool; 100 motor drive controller; 211, 221 accelerationsensor.

The invention claimed is:
 1. A numerical control system that controlsmachine drive systems included in a machine tool that performs machiningusing a tool, according to a numerical control program, the systemcomprising: processing circuitry to acquire a disturbance force or adisturbance torque applied to each of the machine drive systems, andcoordinate-transform the disturbance force or the disturbance torqueinto a tool reference coordinate system for output; and to calculatecutting process parameters that determine characteristics of a cuttingprocess model and dynamic characteristic parameters that determinecharacteristics of a dynamics model of the machine tool, using thedisturbance force or the disturbance torque output, states of themachine drive systems, predetermined equation models, and cuttingconditions, wherein the equation models define relationships between thecutting process parameters, the dynamic characteristic parameters, andthe disturbance force or the disturbance torque, and the processingcircuitry is further configured to correct commands of the numericalcontrol program based on a simulation of the dynamics model and thecutting process model.
 2. The numerical control system according toclaim 1, wherein the processing circuitry acquires the disturbance forceor the disturbance torque from a detection result detected by a sensorto detect a disturbance force or a disturbance torque applied to each ofthe machine drive systems.
 3. The numerical control system according toclaim 1, wherein the processing circuitry further estimates thedisturbance force or the disturbance torque applied to each of themachine drive systems, using a detection result detected by one or moresensors each of which to detect velocity or acceleration ofcorresponding one of the machine drive systems, wherein the processingcircuitry acquires the disturbance force or the disturbance torque. 4.The numerical control system according to claim 1, wherein when thedisturbance forces or the disturbance torques acquired includecomponents in the same direction on tool reference coordinates, theprocessing circuitry selects a combination in which directions areindependent from each other from the disturbance forces or thedisturbance torques acquired.
 5. The numerical control system accordingto claim 3, wherein one of the machine drive systems includes a firststructure and a second structure including a motor, the processingcircuitry calculates an actual power of machine drive system that is aresultant of forces applied to the first structure, based on a pluralityof first structure models of the first structure and the detectionresult, calculates a command power of machine drive system that is aforce applied by the motor to the one of the machine drive systems,based on a second structure model of the second structure, a detectionresult of a motor current flowing through the motor, and a detectionresult of a position of the motor, and estimates the disturbance forceor the disturbance torque using actual power of machine drive system andthe power command of machine drive system, and the plurality of firststructure models have different frequency characteristics determinedaccording to a plurality of divided frequency bands.
 6. The numericalcontrol system according to claim 3, wherein one of the machine drivesystems includes a first structure and a second structure including amotor, the processing circuitry calculates an actual power of machinedrive system that is a resultant of forces applied to the firststructure, based on a first structure model of the first structure andthe detection result, calculates a power command of machine drive systemthat is a force applied by the motor to the one of the machine drivesystems, based on a second structure model of the machine drive systemincluding the motor of the machine drive system, a detection result of amotor current flowing through the motor, and a detection result of aposition of the motor, and estimates the disturbance force or thedisturbance torque using the actual power of machine drive system andthe power command of machine drive system, and one of the structuresconstituting the one of the machine drive systems is divided into afirst inertial body model and a second inertial body model for modeling,the first structure model includes the first inertial body model, andthe second structure model includes the second inertial body model. 7.The numerical control system according to claim 5, wherein theprocessing circuitry corrects time lags produced between a signalindicating the detection result of the motor current, a signalindicating the detection result of the position of the motor, and asignal indicating the detection result of the sensor, and estimates thedisturbance force or the disturbance torque, using the signals correctedin the time lags.
 8. The numerical control system according to claim 1,wherein one of the machine drive systems includes a first structure anda second structure including a motor, the numerical control systemfurther includes a function to simulate a cutting force produced betweenthe tool and a workpiece machined by the tool, based on a detectionresult of a motor current flowing through the motor, a detection resultof a position of the motor, the cutting conditions, and the cuttingprocess model, and simulate a disturbance force or a disturbance torqueproduced at each of the machine drive systems and a relative positiondeviation between the tool and the workpiece when a cutting force isproduced, based on the dynamics model.
 9. The numerical control systemaccording to claim 8, wherein the processing circuitry calculates adifference between the disturbance force output and the disturbanceforce simulated, or a difference between the disturbance torque outputand the disturbance torque simulated, and calculates the cutting processparameters and the dynamic characteristic parameters when the calculateddifference is larger than a threshold.
 10. The numerical control systemaccording to claim 8, wherein the processing circuitry further issues aninstruction to execute calculation of the cutting process parameters andthe dynamic characteristic parameters when the numerical control programincludes a command that instructs execution of identification.
 11. Thenumerical control system according to claim 10, wherein the processingcircuitry corrects commands for the machine drive systems according toresults simulated.
 12. The numerical control system according to claim1, wherein the cutting process model is a mathematical model forcalculating an uncut chip thickness based on a tool rotation angle and arelative displacement between a tooth edge of the tool and a workpiecemachined by the tool, and calculating a cutting force produced based onthe uncut chip thickness between the tool and the workpiece, and thedynamics model is a mathematical model for calculating disturbanceforces or disturbance torques transmitted to the machine drive systemsthrough mechanical structures including the tool or the workpiece whenthe cutting force is produced, and calculating position deviationsproduced at the machine drive systems through the mechanical structureswhen the cutting force is produced.
 13. The numerical control systemaccording to claim 12, wherein the cutting process model is a model inwhich the uncut chip thickness is calculated based on a differencebetween a trajectory formed by a tooth edge of the tool involved incutting and a previous machined surface formed by a tooth edge one ormore teeth before the tooth edge involved in cutting.
 14. The numericalcontrol system according to claim 12, wherein the cutting process modelis a model in which a correction amount corresponding to a numberindicating the tooth edge of the tool and a rotation angle of the tool,is added to or subtracted from the uncut chip thickness.
 15. Thenumerical control system according to claim 12, wherein the cuttingprocess model is a model in which it is determined whether the toothedge contacts the workpiece based on the position deviation at eachrotation angle of the tool or time, and when the tooth edge contacts theworkpiece, the uncut chip thickness is calculated, and when the toothedge does not contact the workpiece, the uncut chip thickness iscalculated to zero.
 16. The numerical control system according to claim6, wherein the processing circuitry corrects time lags produced betweena signal indicating the detection result of the motor current, a signalindicating the detection result of the position of the motor, and asignal indicating the detection result of the sensor, and estimates thedisturbance force or the disturbance torque, using the signals correctedin the time lags.